RE: [PATCH 3/4] mdev: Expose mdev alias in sysfs tree

[Parav Pandit]

> -----Original Message-----
> From: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Sent: Tuesday, August 27, 2019 7:24 AM
> To: Parav Pandit <parav@xxxxxxxxxxxx>
> Cc: Jiri Pirko <jiri@xxxxxxxxxxxx>; kwankhede@xxxxxxxxxx;
> cohuck@xxxxxxxxxx; davem@xxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH 3/4] mdev: Expose mdev alias in sysfs tree
> 
> On Mon, 26 Aug 2019 15:41:18 -0500
> Parav Pandit <parav@xxxxxxxxxxxx> wrote:
> 
> > Expose mdev alias as string in a sysfs tree so that such attribute can
> > be used to generate netdevice name by systemd/udev or can be used to
> > match other kernel objects based on the alias of the mdev.
> >
> > Signed-off-by: Parav Pandit <parav@xxxxxxxxxxxx>
> > ---
> >  drivers/vfio/mdev/mdev_sysfs.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> >
> > diff --git a/drivers/vfio/mdev/mdev_sysfs.c
> > b/drivers/vfio/mdev/mdev_sysfs.c index 43afe0e80b76..59f4e3cc5233
> > 100644
> > --- a/drivers/vfio/mdev/mdev_sysfs.c
> > +++ b/drivers/vfio/mdev/mdev_sysfs.c
> > @@ -246,7 +246,20 @@ static ssize_t remove_store(struct device *dev,
> > struct device_attribute *attr,
> >
> >  static DEVICE_ATTR_WO(remove);
> >
> > +static ssize_t alias_show(struct device *device,
> > +			  struct device_attribute *attr, char *buf) {
> > +	struct mdev_device *dev = mdev_from_dev(device);
> > +
> > +	if (!dev->alias)
> > +		return -EOPNOTSUPP;
> 
> Wouldn't it be better to not create the alias at all?  Thanks,
> 
In other subsystem such as netdev sysfs files are always created that returns either returns EOPNOTSUPP or attribute value.
I guess overhead of create multiple groups or creating individual sysfs files outweigh the simplify of single group.
I think its ok to keep it simple this way.

> Alex
> 
> > +
> > +	return sprintf(buf, "%s\n", dev->alias); } static
> > +DEVICE_ATTR_RO(alias);
> > +
> >  static const struct attribute *mdev_device_attrs[] = {
> > +	&dev_attr_alias.attr,
> >  	&dev_attr_remove.attr,
> >  	NULL,
> >  };